The invention relates to a carrier element for a semiconductor chip with at least two connections, in particular for incorporation into smart cards, the element having an encapsulation composition encapsulating and protecting the semiconductor chip. The connections are made of a conductive material and have a reduced thickness at connection ends facing one another. In addition, the connections have a cross section having a step formed only on one side. The semiconductor chip is disposed on the connections in a region of this section of reduced thickness and is mechanically connected to the connections.
A carrier element is disclosed in JP08 -116016 A from Patent Abstracts of Japan. This known carrier element is not suitable for incorporation into smart cards, however, since it is provided with encapsulation composition on both sides and the connections are not suitably accessible.
Carrier elements for a semiconductor chip for incorporation into smart cards have been disclosed in a wide variety of ways. U.S. Pat. No. 5,134,773 discloses a carrier element with contact areas composed of a conductive material in the form of a so-called lead frame, in which the semiconductor chip is bonded onto a centrally disposed chip island and is electrically connected to peripherally disposed contact areas by bonding wires. The semiconductor chip is surrounded by an encapsulation composition that protects it and the bonding wires and, moreover, holds the contact areas in their position. Since the contact areas have to be freely accessible from the side that is remote from the chip, the encapsulation composition is present only on one side. In order, nevertheless, to afford good mechanical retention, the contact areas have undercuts, on the side remote from the chip, in the region of the slots which electrically insulate them from one another, which undercuts are filled by the encapsulation composition and realize a kind of riveted connection.
Although the carrier element described in U.S. Pat. No. 5,134,773 is configured for so-called smart cards with contacts, that is to say it has contact areas which are situated on a surface of the smart card and are externally accessible to a reading device, it is readily possible, and also known, to provide only two connections which can be electrically connected to a coil disposed in the card or on a card inlay.
In addition, it is possible to provide connections in such numbers and with such a configuration that they are equally suitable for connection both to a coil or antenna and to a reading device.
During the production of contactless smart cards using lamination technology formed of a coil carrier sheet onto which the carrier element is mounted and welded with at least two covering sheets, it is important for the carrier element that is to be covered by the lamination, and which may be regarded as a foreign body, to be configured geometrically to be as small as possible in order to enable the covering sheets, which are softened under temperature and pressure, to flow optimally around the carrier element and thus to achieve a high-quality card without any sunken locations and scattered print, in other words to achieve planar surfaces for subsequent printing.
A typical structure for a smart card for contactless application is built up as follows. The coil carrier sheet has a thickness of approximately 200 xcexcm, the two core sheets have a thickness of approximately 100 xcexcm in each case, two printing sheets on both sides have a thickness of approximately 150 xcexcm in each case, and two scratch-protection sheets have a thickness of approximately 50 xcexcm in each case. The resultant thickness is approximately 800 xcexcm in accordance with the ISO Standard 7816. This results in the carrier element necessarily having a height of less than 400 xcexcm as well as the smallest possible extent in the card plane.
In the case of a realization of the carrier element disclosed in U.S. Pat. No. 5,134,773 the resulting height is more than 400 xcexcm, on account of the mounting of the chip on a chip island and the loop height of the bonding wires.
It is accordingly an object of the invention to provide a carrier element for a semiconductor chip for incorporation into smart cards which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which has a small height and also an improved breaking behavior and, at the same time, is simple to produce.
With the foregoing and other objects in view there is provided, in accordance with the invention, in combination with a semiconductor chip, a carrier element, including:
an encapsulation composition having main surfaces and opposite edges and encapsulating and protecting the semiconductor chip;
at least two connections disposed on one of the main surfaces of the encapsulation composition along only two of the opposite edges, the at least two connections are made of a conductive material and have embossed ends facing one another and with a reduced thickness at the embossed ends and with a cross section having a step only on one side of the at least two connections; and
the semiconductor chip is disposed on the at least two connections in a region of the reduced thickness and are mechanically connected to the at least two connections which results in mechanical connections.
The connections, which are part of a holding frame, a so-called lead frame, during the mounting of the semiconductor chip and the encapsulation of the chip and of the connecting lines, have a section which has a smaller thickness in such a way that the cross section has a step only on one side. The section which has the smaller thickness is produced by embossing in a manner according to the invention. In this case, a reduction in the thickness to 50% of the nominal connection thickness is sufficient for most cases.
Therefore, a main surface of the connections is flat while the opposite surface has a step. The semiconductor chip is disposed in the region of this section. It may be disposed on the side of the step or else on the opposite side. It is expedient for the chip to be mounted with its active side oriented away from the connections if it is disposed on the step side of the connections. If it is disposed on the side opposite to the step side, it is advantageous if the chip is mounted with its active side oriented toward the connections, since the bonding wires can then be connected to the connections in the region of the sections having the small thickness and, consequently, the loop height of the bonding wires is no longer significant. The desired height saving is produced in both cases.
The largest possible height saving can be obtained by using so-called flip-chip mounting, in which the semiconductor chip is soldered or bonded onto the connections directly by its terminal pads, which are advantageously provided with elevations, so-called xe2x80x9cbumpsxe2x80x9d. This makes it possible to dispense with bonding wires.
Dispensing with a chip island has not only the advantage of a smaller thickness of the carrier element but also that of better anchoring of the encapsulation composition together with the connections, since the encapsulation composition can enclose the chip from both sides and there is a good connection between the chip and the connections. The obviation of the chip island results in that notch effect forces no longer occur either, thereby resulting in better breaking strength properties.
On account of the small height desired for the carrier element, one of the connection surfaces will be exposed and available for contact-making. For the best possible incorporation into a smart card, in particular into a laminated smart card, it is advantageous if the encapsulation composition situated between the connections is flush with the surface of the connections.
The connections may project beyond the dimensions of the encapsulation composition and form contact lugs there for antenna connections. This is advantageous for mounting in the course of which an antenna coil is applied on a carrier sheet. The carrier sheet advantageously has a cutout or recess in which the encapsulation composition is situated, while the connections or, in this case, the contact lugs are situated on the coil carrier sheet on coil connections.
However, it is likewise possible for the connections to be provided only in the region of the encapsulation composition, this having the advantage that such a carrier element can also be inserted subsequently into an already laminated card, which has a cutout, however. In an expedient manner, the ends of the antenna coil will be situated in this cutout in order to be able to be connected in a simple manner to the carrier element connections, for example by bonding or soldering or else by use of resilient connecting parts.
A carrier element that has only such contact areas instead of contact lugs projecting beyond the edge can, however, also be applied directly to a coil carrier sheet. In this case, the corresponding core sheet of the card laminate should have a cutout.
The contact lugs can advantageously have a widened end in order to be able to be connected better to connections of wound coils.
Particularly good anchoring of the encapsulation composition together with the connections is achieved if the connections are bent at a right angle toward the chip and, consequently, the angular regions are situated in the encapsulation composition. If the connections lugs are once again bent at a right angle, preferably in the other direction, even better anchoring is produced. Moreover, further contact areas are produced in this way and can be utilized for alternative mounting.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a carrier element for a semiconductor chip for incorporation into smart cards, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.